Final Fantasy XIII-2 weighs in at 14.446 gigabytes on PlayStation 3 and 7.8 gigabytes on Xbox 360, according to a 2ch poster.
To compare, Final Fantasy XIII weighed 37.6 gigabytes on PlayStation 3 and 18.3 gigabytes on Xbox 360.
The difference in filesize, similar to the first game, is most likely due to the Bink Video compression seen in the Xbox 360 version.
Thanks, Erren.